Hemoglobin Riyadh--alpha2beta2 (120(GH3)Lys replaced by Asn). A new variant found in association with alpha-thalassemia and iron deficiency

Molecular nature of alpha-globin genes in the Saudi population

Alpha-thalassemia (α-thal) is a disorder caused by the deletion of single or double α-globin genes, and/or point mutations in the α-globin genes. There are 2 common types of α-globin genes; HBA2 and HBA1. Recently, it has been discovered that the HBA2 gene is replaced by a unique HBA12 gene convert in 5.7% of the Saudi population. The α-globin genes have been emerging as a molecular target for the treatment of β-thalassemia (β-thal). Hence, it is essential to understand the molecular nature of α-globin genes to treat the most prevalent hemoglobin disorders, such as sickle cell disease, α-thal, and β-thal prevalent in the Kingdom of Saudi Arabia. Thirty-two different α-globin genotypes have been observed in the Saudi population. This review outlines the classification of the α-globin genes on the basis of their molecular nature and complex combinations of α-globin genes, and their variants predominant in Saudis.

Genome at juncture of early human migration: a systematic analysis of two whole genomes and thirteen exomes from Kuwaiti population subgroup of inferred Saudi Arabian tribe ancestry

Population of the State of Kuwait is composed of three genetic subgroups of inferred Persian, Saudi Arabian tribe and Bedouin ancestry. The Saudi Arabian tribe subgroup traces its origin to the Najd region of Saudi Arabia. By sequencing two whole genomes and thirteen exomes from this subgroup at high coverage (>40X), we identify 4,950,724 Single Nucleotide Polymorphisms (SNPs), 515,802 indels and 39,762 structural variations. Of the identified variants, 10,098 (8.3%) exomic SNPs, 139,923 (2.9%) non-exomic SNPs, 5,256 (54.3%) exomic indels, and 374,959 (74.08%) non-exomic indels are 'novel'. Up to 8,070 (79.9%) of the reported novel biallelic exomic SNPs are seen in low frequency (minor allele frequency <5%). We observe 5,462 known and 1,004 novel potentially deleterious nonsynonymous SNPs. Allele frequencies of common SNPs from the 15 exomes is significantly correlated with those from genotype data of a larger cohort of 48 individuals (Pearson correlation coefficient, 0.91; p <2.2×10-16). A set of 2,485 SNPs show significantly different allele frequencies when compared to populations from other continents. Two notable variants having risk alleles in high frequencies in this subgroup are: a nonsynonymous deleterious SNP (rs2108622 [19:g.15990431C>T] from CYP4F2 gene [MIM:*604426]) associated with warfarin dosage levels [MIM:#122700] required to elicit normal anticoagulant response; and a 3' UTR SNP (rs6151429 [22:g.51063477T>C]) from ARSA gene [MIM:*607574]) associated with Metachromatic Leukodystrophy [MIM:#250100]. Hemoglobin Riyadh variant (identified for the first time in a Saudi Arabian woman) is observed in the exome data. The mitochondrial haplogroup profiles of the 15 individuals are consistent with the haplogroup diversity seen in Saudi Arabian natives, who are believed to have received substantial gene flow from Africa and eastern provenance. We present the first genome resource imperative for designing future genetic studies in Saudi Arabian tribe subgroup. The full-length genome sequences and the identified variants are available at ftp://dgr.dasmaninstitute.org and http://dgr.dasmaninstitute.org/DGR/gb.html.

Molecular analysis of beta-thalassaemia patients in a high incidence area of southern Italy

The prevalence of eight mutations in 84 patients with beta-thalassaemia major and in 16 subjects with thalassaemia intermedia was investigated. All of the patients were Italian, originating from Eastern Sicily (Messina area) and some Calabrian regions. Genomic DNA was amplified by polymerase chain reaction (PCR). DNA molecular investigations were performed by allele-specific oligonucleotide (ASO) hybridization, to identify the following beta-thalassaemia mutations: CD39 (C-T), IVS1-110 (G-A), IVS1-6 (T-C), IVS1-1 (G-A), IVS2-745 (C-G), IVS2-1 (G-A), -87 (C-G), CD6 A (-A). Our data underline that in thalassemia intermedia two mutations were statistically prevalent: IVS1-6 T-->C (P < 0.001) and CD 6-A (P < 0.05). CD 39 was statistically prevalent in beta-thalassaemia major patients (P < 0.01). The difference between the two groups was not statistically significant for all the other mutations. Five different genotypes were recorded among thalassaemia intermedia and 15 among beta-thalassaemia major patients. Twenty-five percent of the intermedia patients and 4.5% of the major patients had homozygosity for mild mutations (group I); 62.5% of the intermedia patients and 26.2% of the major patients had combinations of mild/severe mutations (group II). In addition, homozygosity or double heterozygosity for severe mutations (group III) was found in 12.5% of the intermedia patients and 69% of the major patients. Some genotypes were restricted to thalassaemia intermedia, including heterozygosity -87/IVS1-6 and IVS1-6/CD 6-A. It is essential to understand the distribution and frequency of the relevant mutations in each population where beta-thalassaemias exist. This is of particular importance for genotype-phenotype correlation and for carrier detection, genetic counselling and prenatal diagnosis.

Fetal haemoglobin level--effect of gender, age and haemoglobin disorders

Fetal haemoglobin (Hb F) levels shows significant variations in health and disease states. In this study we investigated Hb F level in 75 cord bloods, 1266 healthy individuals, 1582 Hb S heterozygotes, 464 sickle cell anaemia, 93 Hb S/beta(0) -thalassaemia and 65 beta-thalassemia major patients. The age range of the study groups varied from newborn to over 60 years of age. Hb F level was measured by an alkali denaturation procedure and by radial immunodiffusion. The ratio of the level of G gamma-globin chains to the level of A gamma-globin chains (G gamma/A gamma) was determined in the patients group by high performance liquid chromatography. The Hb F level was significantly higher in the sickle cell anaemia and beta-thalassemia major patients compared to the Hb S heterozygotes and the normal individuals. Within each group Hb F level was higher in the female population compared to the age-matched male groups. This difference was statistically significant (P < 0.05) in the sickle cell disease patients and beta-thalassemia major patients but not in the normal individuals. After the age of 30 years, the difference in the value of Hb F in the male and female population become more apparent (P < 0.05) in the sickle cell disease and beta-thalassaemia major patients. No statistically significant sex differences were found in the G gamma/A gamma ratio in the patient groups, and the range of G gamma/A gamma ratio in the patients groups were similar to those in the control group. The results showed that age, sex and genetic disorders of haemoglobin are factors that affect Hb F level and indicate the possible involvement of an X-linked factor in control of Hb F production.

Hemoglobin takamatsu (beta 120 (GH 3) Lys leads to Gln): a new abnormal hemoglobin detected in three unrelated families in the takamatsu area of shikoku

A survey of hemoglobinopathies which was carried out in the Takamatsu district during the period from January to August 1979 detected six families with abnormal hemoglobins. Approximately 6010 inhabitants were screened. Three of these families had the same new Hb variant (Hb Takamatsu beta 120 Lys leads to Gln) that has not been previously reported. Existence of a blood relationship among these three families could not be established even after careful family studies. This abnormal hemoglobin was not associated with adverse symptoms and gave normal hematologic findings in the carriers. The isopropranol test was negative, oxygen affinity was within the normal range, and biosynthetic ratio in reticulocytes was around 1.0. One of the difficulties in the structural analysis of this hemoglobin was related to complete superposition of abnormal beta XT-12b,13 on a beta T-8,9 peptide in the fingerprint of the trypsin digest of aminoethylated aberrant beta X chain. This was overcome by collection of abnormal tryptic beta core (beta XT-10-13) from unmodified beta X chain, and subsequent digestion by chymotrypsin. Edman analysis of the chymotryptic peptides thus obtained successfully confirmed the substitution to be beta 120 Lys leads to Gln.

Separation of tryptic peptides of normal and abnormal alpha, beta, gamma, and delta hemoglobin chains by high-performance liquid chromatography

High-performance liquid chromatography (HPLC) was used to separate tryptic peptides of the normal alpha, beta, gamma, and delta chains of human hemoglobins A, F, and A2 and of the abnormal chains of 25 hemoglobin variants. In addition, the separation of chymotryptic peptides of the oxidized core of the normal alpha chain by HPLC was evaluated. HPLC has several advantages over conventional methods used for the separation of proteolytic fragments of hemoglobin chains. The method is fast, and reproducible, and requires only small quantities of material. Several peptides are eluted as single zones, thus eliminating the need of rechromatography for further purification. Characteristic changes in the elution pattern of the peptides often indicate specific modifications.

On the nature of sickle-cell disease in the Arabian Peninsula

The sickle-cell gene contributes substantially to the presentation of anaemia in certain areas of the Arabian Peninsula. However, the clinical presentation of the homozygous state of Hb S is less severe than that observed in other ethnic groups, such as American negroes. In the present paper, biosynthesis studies performed on reticulocytes from heterozygotes and homozygotes for the Hb S give further indications of the mild nature of sickle-cell disease in Arabia. Comparison of two affected families, from Saudi Arabia and Jordan, showed that clinical manifestation of the disease is mirrored by the biochemical and haematological findings in affected individuals. The results are discussed in terms of the effect of co-existing thalassaemia and/or iron deficiency with Hb S. It is suggested that both genetic and acquired conditions play a role in the clinical features of the disease. The mechanisms responsible for regulation of alpha-chain synthesis by iron (haem) deficiency are discussed.

Hemoglobin Riyadh-beta 0-thalassemia in an Indian family

An Indian (Asian) patient with compound heterozygosity for Hb Riyadh and beta 0-thalassemia is described. Hb Riyadh forms about 95% of the hemoglobin present. The clinico-pathological picture is identical to that of simple beta-thalassemia trait confirming the harmless nature of the substitution beta 120(GH3) Lys leads to Asn.

Hemoglobin Karatsu: beta 120 (GH 3) lysine leads to asparagine, an example of HB Riyadh in Japan

Hemoglobin Karatsu was discovered in a Japanese male during a random survey of patients. Fingerprints of aminoethylated beta chain revealed an abnormal beta Tp12B-13 spot. Further chemical analyses and comparison with the corresponding tryptic peptide from Hb Hijiyama demonstrated an identical amino acid substitution with Hb Riyadh.